The radio access network (RAN), system architecture (SA) and the core terminal (CT) working groups of the third generation partnership project (3GPP) aim to develop an enhanced UTRAN (E-UTRAN) architecture for next generation wireless systems. The E-UTRAN system is required to co-exist with the current second (2G), third generation (3G) wireless systems and non-3GPP networks namely cdma2000 and WiMAX and in particular, support handovers between the existing systems and the newly evolved E-UTRAN system, specified in the 3GPP TR 23.882, 3GPP TS 23.401 and 3GPP TS 23.402.
The E-UTRAN system is an evolution of the 3GPP UTRAN system, in which the main entities are the user equipment (UE), the enhanced Node B (ENB), Mobility Management Entity (MME), serving gateway and PDN GW as shown in the FIG. 1. The ENB of the EUTRAN system is expected to have the features of the Node B and the radio network controller (RNC) of the legacy UTRAN system. MME of the System Architecture Evolution (SAE) manages and stores UE context (for idle state: UE/user identities, UE mobility state, user security parameters). It generates temporary identities and allocates them to UEs. It checks the authorization whether the UE may camp on the TA or on the PLMN. It also authenticates the user. Serving gateway of SAE terminates for idle state UEs the downlink data path and triggers/initiates paging when downlink data arrive for the UE. PDN GW is the user plane anchor for mobility between different access systems. It performs or supports handover between different access systems.
The GERAN consists of the Base Transceiver Station (BTS) and the Base Station Controller (BSC). The UTRAN consists of the Node B and the Radio Network Controller (RNC). The GPRS Core Network consists of the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN) as shown in FIG. 1.
The integrated WLAN (I-WLAN) system specified in the 3GPP TS 23.234 specifications provides a system and method to integrate legacy UTRAN systems with WLAN systems. The I-WLAN system allows WLAN users to access 3GPP packet switched services.
The concept of a serving network entity taking a decision for the inter-RAT handover has been disclosed in the patent application US 2007/0218903. However, the patent application does not mention handover decision based on target access system handover criteria, information related to target access system ranking, and the capability to assess target access system signal measurement reports. Further, the patent application also does not explicitly mention that the decision of handover is being taken in a hierarchical manner.